[Diy_efi] Frustrating fuel delivery problem!

David Cooley n5xmt at bellsouth.net
Mon Jan 17 19:41:21 GMT 2005 

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 My first thought is the tank isn't vented properly and you are pulling a
vacuum on the tank...  Try it around the block with the gas cap off and s=
ee
what happens...=0D
=0D
 =0D
-------Original Message-------=0D
 =0D
From: charlesmorris at direcway.com=0D
Date: 01/17/05 14:08:50=0D
To: diy_efi at diy-efi.org=0D
Subject: [Diy_efi] Frustrating fuel delivery problem!=0D
 =0D
This EFI system is driving me crazy. I can't fix it and don't know why. A=
ny
help greatly appreciated.=0D
 =0D
Car is an '81 BMW 745i (factory intercooled turbo 3.2 liter, Bosch
L-Jetronic system, six 270 cc/min @ 36 psi injectors) that has been
extensively modified. The engine is now 3.5 liters and stock 7 psi boost
level is now 15 psi. I added two large 600cc/min injectors mounted just
upstream of the throttle, controlled by a homemade 8-bit microprocessor.=0D
 =0D
The fuel system details:=0D
#8 power cable directly from battery to trunk for stereo, tapped under ba=
ck
seat for fuel pump feed, relay controlled by original fuel pump wiring wh=
ich
was way too small.=0D
Bosch 10208 (large) pump to drive original injectors through #6 Teflon
braided line=0D
Original Bosch pump feeding the supplemental injectors through #4 Teflon
line=0D
#6 Teflon return line=0D
Earl's "screen" prefilter in suction side of each pump=0D
Earl's sintered bronze filter in pressure side of each line=0D
Eliminated transfer pump. Made "Y" pickup with 1/2" copper tubing and
original pickup "sock".=0D
Stock tank 100 liter/26 gal.=0D
Increased fuel pressure from 2.5 to 3 bar (43 psi).=0D
Single "Fogger" nitrous system (20-40hp for quicker spool-up, fuel taken
from main rail).=0D
 =0D
I used to drive this car daily, sometimes to "closed course only" 140+
speeds, and *never* had a fuel delivery problem. Then it sat in a barn fo=
r
three years and everything steel under the trunk rusted out completely
including the gas tank. I replaced it, unknowingly pinching the flex line=
s
from the pickup to the suction filters nearly closed (more on this later)=
 -
but never drove the car further than the driveway until this year.=0D
 =0D
Once I started driving it again, it was obvious that there was a fuel
delivery problem. It would not make more than a couple of lbs. boost and
would start misfiring badly above 3500 rpm under any positive manifold
pressure. It gradually got worse (can't floor it above 2000 rpm or it sta=
rts
bucking) to the point where I started fixing it. The filters were plugged
with rust and varnish. Still no good. Replaced big Bosch pump with an MSD
2255. No good. Finally found the pinched intake lines and replaced them w=
ith
1/2" aluminum hardline. STILL no good!=0D
 =0D
Added a fuel pressure gauge to the dash and consistently whenever it's
bucking the fuel pressure is dropping like a rock and will go to zero if
pedal held down far enough and long enough. Discovered the inline 40A fus=
e
holder was defective (getting warm to the touch, 0.6 volt drop with the c=
ar
idling and half-melted the solder on one end of the fuse). Jumpered it ou=
t.
Resoldered original control relay ("main relay") terminals on its interna=
l
PC board, a known weak spot on these cars. Now, steady 13.05 volts under =
the
back seat (18" 12ga. wire from there to the pair of pumps). Ground wire
intact and clean, no drop to body. Volts steady regardless of pressure or
how severe the bucking. Still not fixed!=0D
 =0D
Tried yet another pump (Walbro 255 LPH). Not fixed. No obvious pinch or k=
ink
anywhere in the lines from pickup (siphons freely when disconnected). Can
blow through filters. Screens are visibly clear. Confirmed by measuring f=
low
from return line, only has a few hundred cc in 30 sec. with engine off, 4=
3
psi at the rail, not nearly the liter per 20 seconds expected.=0D
 =0D
I can't think of anything else. The system is only a hose, pump, and wire=
s,
for crying out loud!=0D
I would have thought that the transfer pump was required except that with
two fuel pumps going, it wouldn't be big enough anyway and would be an
obstruction. And it USED TO WORK. It does self-prime, by the way. Tank fu=
el
level makes no difference. Additional injector rail is steady on 36 psi,
haven't bothered to check that system's return rate yet since the main
system isn't right.=0D
 =0D
WHAT else can I look for?? I'm pulling out my hair.=0D
 =0D
thanks=0D
Charles=0D
 =0D
 =0D
_______________________________________________=0D
diy_efi mailing list=0D
diy_efi at diy-efi.org=0D
http://lists.diy-efi.org/mailman/listinfo/diy_efi
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<DIV>&nbsp;My first thought is the tank isn't vented properly and you are=
 pulling a vacuum on the tank...&nbsp; Try it around the block with the g=
as cap off and see what happens...</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV id=3DIncrediOriginalMessage><I>-------Original Message-------</I></D=
IV>
<DIV>&nbsp;</DIV>
<DIV id=3Dreceivestrings>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt"><I><B>From:</B></I> <A href=3D"m=
ailto:charlesmorris at direcway.com">charlesmorris at direcway.com</A></DIV>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt"><I><B>Date:</B></I> 01/17/05 14:=
08:50</DIV>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt"><I><B>To:</B></I> <A href=3D"mai=
lto:diy_efi at diy-efi.org">diy_efi at diy-efi.org</A></DIV>
<DIV dir=3Dltr style=3D"FONT-SIZE: 11pt"><I><B>Subject:</B></I> [Diy_efi]=
 Frustrating fuel delivery problem!</DIV></DIV>
<DIV>&nbsp;</DIV>
<DIV>This EFI system is driving me crazy. I can't fix it and don't know w=
hy. Any help greatly appreciated.</DIV>
<DIV>&nbsp;</DIV><A href=3D"mailto:<DIV>Car is an '81 BMW 745i (factory i=
ntercooled turbo 3.2 liter, Bosch L-Jetronic system, six 270 cc/min @">
<DIV>Car is an '81 BMW 745i (factory intercooled turbo 3.2 liter, Bosch L=
-Jetronic system, six 270 cc/min @</A> 36 psi injectors) that has been ex=
tensively modified. The engine is now 3.5 liters and stock 7 psi boost le=
vel is now 15 psi. I added two large 600cc/min injectors mounted just ups=
tream of the throttle, controlled by a homemade 8-bit microprocessor.</DI=
V>
<DIV>&nbsp;</DIV>
<DIV>The fuel system details:</DIV>
<DIV>#8 power cable directly from battery to trunk for stereo, tapped und=
er back seat for fuel pump feed, relay controlled by original fuel pump w=
iring which was way too small.</DIV>
<DIV>Bosch 10208 (large) pump to drive original injectors through #6 Tefl=
on braided line</DIV>
<DIV>Original Bosch pump feeding the supplemental injectors through #4 Te=
flon line</DIV>
<DIV>#6 Teflon return line</DIV>
<DIV>Earl's "screen" prefilter in suction side of each pump</DIV>
<DIV>Earl's sintered bronze filter in pressure side of each line</DIV>
<DIV>Eliminated transfer pump. Made "Y" pickup with 1/2" copper tubing an=
d original pickup "sock".</DIV>
<DIV>Stock tank 100 liter/26 gal.</DIV>
<DIV>Increased fuel pressure from 2.5 to 3 bar (43 psi).</DIV>
<DIV>Single "Fogger" nitrous system (20-40hp for quicker spool-up, fuel t=
aken from main rail).</DIV>
<DIV>&nbsp;</DIV>
<DIV>I used to drive this car daily, sometimes to "closed course only" 14=
0+ speeds, and *never* had a fuel delivery problem. Then it sat in a barn=
 for three years and everything steel under the trunk rusted out complete=
ly including the gas tank. I replaced it, unknowingly pinching the flex l=
ines from the pickup to the suction filters nearly closed (more on this l=
ater) - but never drove the car further than the driveway until this year=
=2E</DIV>
<DIV>&nbsp;</DIV>
<DIV>Once I started driving it again, it was obvious that there was a fue=
l delivery problem. It would not make more than a couple of lbs. boost an=
d would start misfiring badly above 3500 rpm under any positive manifold =
pressure. It gradually got worse (can't floor it above 2000 rpm or it sta=
rts bucking) to the point where I started fixing it. The filters were plu=
gged with rust and varnish. Still no good. Replaced big Bosch pump with a=
n MSD 2255. No good. Finally found the pinched intake lines and replaced =
them with 1/2" aluminum hardline. STILL no good!</DIV>
<DIV>&nbsp;</DIV>
<DIV>Added a fuel pressure gauge to the dash and consistently whenever it=
's bucking the fuel pressure is dropping like a rock and will go to zero =
if pedal held down far enough and long enough. Discovered the inline 40A =
fuse holder was defective (getting warm to the touch, 0.6 volt drop with =
the car idling and half-melted the solder on one end of the fuse). Jumper=
ed it out. Resoldered original control relay ("main relay") terminals on =
its internal PC board, a known weak spot on these cars. Now, steady 13.05=
 volts under the back seat (18" 12ga. wire from there to the pair of pump=
s). Ground wire intact and clean, no drop to body. Volts steady regardles=
s of pressure or how severe the bucking. Still not fixed!</DIV>
<DIV>&nbsp;</DIV>
<DIV>Tried yet another pump (Walbro 255 LPH). Not fixed. No obvious pinch=
 or kink anywhere in the lines from pickup (siphons freely when disconnec=
ted). Can blow through filters. Screens are visibly clear. Confirmed by m=
easuring flow from return line, only has a few hundred cc in 30 sec. with=
 engine off, 43 psi at the rail, not nearly the liter per 20 seconds expe=
cted.</DIV>
<DIV>&nbsp;</DIV>
<DIV>I can't think of anything else. The system is only a hose, pump, and=
 wires, for crying out loud!</DIV>
<DIV>I would have thought that the transfer pump was required except that=
 with two fuel pumps going, it wouldn't be big enough anyway and would be=
 an obstruction. And it USED TO WORK. It does self-prime, by the way. Tan=
k fuel level makes no difference. Additional injector rail is steady on 3=
6 psi, haven't bothered to check that system's return rate yet since the =
main system isn't right.</DIV>
<DIV>&nbsp;</DIV>
<DIV>WHAT else can I look for?? I'm pulling out my hair.</DIV>
<DIV>&nbsp;</DIV>
<DIV>thanks</DIV>
<DIV>Charles</DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV>_______________________________________________</DIV>
<DIV>diy_efi mailing list</DIV>
<DIV><A href=3D"mailto:diy_efi at diy-efi.org">diy_efi at diy-efi.org</A></DIV>
<DIV><A href=3D"http://lists.diy-efi.org/mailman/listinfo/diy_efi">http:/=
/lists.diy-efi.org/mailman/listinfo/diy_efi</A></DIV></TD></TR>
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